Algal Vegetation of Ponds on Hamfistead Heath. 77 
day in October in 6'. ctecimina (pond II), but the zygotes never 
ripened and all the filaments soon disappeared. The only species 
which could survive the summer without apparent harm was >S. 
adnata in 1912. As in the species discussed by Fritsch, the 
Hampstead Spirogyras appear to thrive best in the bright days 
following heavy rainfall in the late spring or early summer. 
The genus Mougeotia has been represented at some time or 
other in every pond, but never occurs in such abundance as does 
Spirogyra. It is throughout represented by two forms, a large one 
which has never been seen to conjugate (probably M. scalaris) and 
a much smaller species which conjugated to some extent in June, 
1912. In ponds I and II these species together dominated all of 
the other green algae from April to July, 1912, and from February 
to June in 1913. In all the other ponds Mougeotia is distinctly 
secondary to Spirogyra , appearing later, and disappearing earlier : 
it also exhibits a distinct autumn phase. In both of these respects 
the Mougeotias of the Hampstead ponds differ from those observed 
by Fritsch, which were more hardy, appearing first, and lasting 
longer than Spirogyra ; these also had a less decided autumn phase 
than the associated Spirogyra. 
The desmids are represented by the three genera Closterium, 
Staurastrum and Penium. Of these, the first has been found in 
every pond excepting pond I, and at every time of year excepting 
August and September. It is never abundant, but reaches a slight 
maximum from March to May, i.e., rather earlier than the accom¬ 
panying Zygnemacese. In Barton’s Pond 1 the maximum develop¬ 
ment of Closterium was in early summer, following the filamentous 
Conjugate; and in the lakes of the north-west of England, 2 Closterium 
and other Desmidiaceae were most frequent in the latter part of the 
year (June to November). Their occurrence is thus variable, and 
probably the result of local climatic effects. 
On two occasions when samples of algae from the Hampstead 
ponds were kept for months in a large glass jar of water, all the 
animal life, and finally all the plant life, excepting desmids, 
disappeared. At first a mixture of the three forms was found, but 
ultimately Penium dominated the rest, and appears to be able to 
last for months unchanged. It seems to me probable that the 
presence of animal life may well act as a check on the increase or 
these desmids in nature, for I have more than once observed one 
1 Fritsch, F., and Rich, F. Loc. cit., pp. 23-26. 
5 West, W., and West, G. S. Loc. cit. 
